Begin scouting first generation Bean Leaf Beetles one week after the predicted peak emergence of the 1st generation to determine control strategies for the 2nd generation (next month).  Peak 1^st generation emergence will occur around 1212 GDD’s following soybean emergence.

ISU has developed a control strategy (for 2^nd generation beetles in Mid-August and September) based on 1^st generation population numbers. Based upon a high density of first generation beetles, it is expected that the second generation will exceed the economic threshold. This new management concept stops the second-generation beetles long before they reach the old economic threshold.

The first thing to do is determine the date soybeans emerged, then refer to the accumulated GDD graph and match dates. Begin sampling fields 1 week after peak emergence. If the sample is below threshold (Table 1), scout again the next week. If the sample is still below threshold, scout 1 more week. If 1st generation beetles are above threshold, scout again mid August to confirm beetles are present, then spray.

Figure 1.  Degree Day Accumulation for predicting emergence of 1st Generation BLB based on emergence date of the soybean field.

Degree-Day Data as of July 11, 2005

Figure 2.  Overwintered, First and Second generation bean leaf beetle estimated population cycle.

Todd Vagts
Iowa State University Extension
Field Crops Specialist
1240 D. Heires Avenue 
Carroll, IA 51401 
Office: 712-792-2364; Cell: 712-249-6025;  Fax: 712-792-2366
Email: vagts@iastate.edu  

For questions or comments please respond to vagts@iastate.edu

This page last updated on 07/18/05